Why is MAC foundation so popular?

I've seen on a lot of forums, and such like, that people really love MACs SFF foundation. I used it for a year and must say it is absolutely dreadful, and doesn't stay on your skin. I would say I don't have problem skin, it's not naturally oily and it's moisturised well, I often get compliments on it. However, when I used it it made me look disgustingly shiny and made me break out and get dry skin all round my face, it also looks heavy. What I'm wondering is if anyone genuinely feels MAC SFF is a decent foundation. I'm returning my last bottle which I have now replaced with Estee Lauder doublewear which is brilliant.